1. Field of the Invention
The invention in general relates to the field of offshore oil production, and more particularly to a marine riser with an improved liner.
2. Description of Related Art
A typical marine riser is a cylindrical steel pipe or column which is located vertically between the ocean bottom and a drilling vessel at the surface. The riser system is made up of a plurality of sections or joints connected end to end in a string between the surface and the borehole.
In the drilling of a production well, a drill pipe having a drill bit at its end rotates internally within the riser and carries drilling fluid to the drill bit to lubricate the bit, to remove the cuttings from the borehole and to protect the walls of the hole until cased. The riser provides for the return of the drilling fluids back to the supply on the drilling vessel.
Drilling risers used to date are medium strength steel whose weight provides heavy loadings for the drill platform with the loading increasing as the depth of the ocean increases, eventually reaching a practical limit. Various modifications such as the use of flotation devices have been used to extend this depth with a consequent economic penalty in the drilling operation.
The use of lighter weight materials such as titanium or composites for drilling risers would significantly decrease the deck weight of the riser system, would allow for the storage of a greater number of riser sections and would extend the allowable drilling depths for offshore oil production. One such light-weight riser is described and claimed in U.S. Pat. No. 5,439,323. (W.E. 57,706 filed Jul. 9, 1993, Ser. No. 08/089,724)
Extensive use of light-weight composites for marine risers has not been accomplished because of the susceptibility of these light-weight materials to a reduction in strength due to high temperature, chemical corrosives and abrasive contaminants in the drilling fluid, and the wear produced by the rotating drill pipe coming into contact with the riser.
The present invention provides for a solution so as to enable economic use of light-weight materials such as titanium or composites for marine risers.